At 3:38 p.m. on Monday, March 26, 2018, a German tourist called the authorities from the Juan Creek crossing on California’s scenic Highway 1. She had spotted something jarring: a brown sport-utility vehicle, upside down, in the Pacific Ocean.

was trapped between the roof and the seats in the back. Both were dead.

Within about three weeks, the authorities would also discover the remains of four of the Harts’ six children — Markis, 19, Jeremiah, 14, Abigail, 14, and Ciera, 12 — and declare them all dead, too. They eventually discovered skeletal remains inside a woman’s shoe, and announced this month that they belonged to 16-year-old Hannah. Devonte, 15, is still considered to be missing, but is presumed dead.

Jennifer, 38, had been drunk at the time of the crash, and Sarah, 38, and two of their children had in their systems a significant amount of an antihistamine that can cause drowsiness, law enforcement officials said.

Though the central question of why Jennifer Hart drove off the cliff may never be resolved, interviews and more than 1,000 pages of investigative documents released by the authorities in Washington State — where the family last lived — reveal the most vivid picture yet of the Hart family.

They portray Jennifer and Sarah as adoptive mothers under increasing strain, who fled at signs of trouble and closed ranks around their children as scrutiny intensified.

And they show that by that fateful Monday last March, as child welfare officials came knocking, some neighbors, relatives and co-workers were growing alarmed.

“Are you ok?!” one of Sarah’s co-workers texted her two minutes after the German tourist reported the S.U.V. “Please let someone know...we are all freaking out here.”

[Read our initial coverage of the crash]

Law enforcement officials in California have issued only one statement on the case since May, though the investigation continues. Relatives and friends of Jennifer and Sarah declined to comment for this article. Still, the documents illuminate the complicated family dynamics among the Harts — a white couple who adopted six black children, all of whom would perish.

A family grows

Jennifer Jean Hart and Sarah Margaret Gengler grew up about 150 miles apart in South Dakota and met at Northern State University. By 2005, they were living together in Alexandria, Minn.

Investigative documents say they provided foster care for a 16-year-old girl who was removed from their home in February 2006 because of her “suicidal idealizations and threats.” The couple were planning to adopt and said they “didn’t want that negative energy to impact their children,” the documents said.

Markis, Hannah and Abigail were placed with the Harts on March 4, 2006, and their adoption was completed six months later. Within a year, the women spent at least 15 hours training on topics like “racial diversity excitement” and “helping abused kids in care heal,” documents show.

“The Hart family takes every opportunity to celebrate the children’s ethnic heritage,” a caseworker wrote in a report for the Permanent Family Resource Center, a foster care and adoption agency in Fergus Falls, Minn., that later closed after being cited for code violations. The caseworker “whole heartily” recommended that the family be able to adopt a second sibling group.

Jeremiah, Devonte and Ciera were adopted in June 2008, documents show; Jennifer and Sarah married in Connecticut the next year.

In a March 2009 email, Jennifer shared plans for the family’s next step: Sarah is “trying to get pregnant,” she wrote.

“After 10 years of talking about this, we have decided on a donor,” Jennifer wrote. “This month will be the first time she will have done the actual procedure. It’s kind of nervewracking.”

But by July, she wrote to someone else, the doctor “couldn’t find the baby’s heart beat.”

She updated the person six days later: “The baby did not make it.”

Signs of trouble

In an August 2010 email to another woman, Jennifer complained about Sarah, who she said had “said some hurtful things.”

“For quite some time I have felt very under appreciated, and taken for granted in our relationship...and at times unloved,” she wrote. “While I know deep in my heart how much she loves me...she is just horrible about showing it.”

“I have felt that I have been raising the kids on my own,” she added. “I need a ‘break.’”

A few months later, Minnesota Child Welfare received six reports of abuse or neglect by the Harts — two of which it deemed credible. In one episode, Sarah admitted to having physically harmed Abigail. Records show Sarah was convicted of misdemeanor domestic assault.

The family then made its first major move — to West Linn, Ore. — where an anonymous person told officials that the Hart children appeared malnourished. Investigators in Oregon began an inquiry and interviewed women who knew the family and described them as militant parents who imposed harsh disciplinary measures on their children.

[Read more about the reports made to child welfare officials’ and their attempts to intervene.]

But any private turmoil was glossed over by public videos and posts on social media that portrayed a happy, if eccentric, family. YouTube videos posted by Jennifer, for instance, show Devonte dancing and the other children singing, “We are so provided for.”

But at a 2014 demonstration in Portland, Ore., to protest police violence, Devonte was photographed with a pained expression hugging a white police sergeant. The image went viral, and it was time to move again.

Meeting the neighbors

By May 2017 the Harts were living on more than two acres of land in Woodland, Wash. The only two other homes nearby were shrouded by trees and fences.

Bruce and Dana DeKalb lived in one of them. They told investigators that they had been excited to have new neighbors. But they so rarely saw anyone from the property that they initially wondered if a family had in fact moved in.

They had. Around 1:30 a.m. one day in August 2017, Hannah rang the DeKalbs’ doorbell and ran inside their home, the DeKalbs said in interviews. She was missing two teeth and was so thin that they thought the teenager was 6 or 7 years old.

“Can you take me to Seattle?” Mr. DeKalb, 63, recalled her asking.

Hannah said she had jumped out of a second-story window to escape. She explained that she had been whipped and that her mothers were racist, Mr. DeKalb said.

Minutes later, Hannah’s parents showed up at the DeKalbs’ home, and Hannah hid in a bedroom.

Eventually, Ms. DeKalb gave Jennifer time to speak with her daughter alone. After they came downstairs, Hannah apologized, and they went home, Ms. DeKalb said.

Hannah and her family returned the next morning with a written apology. Jennifer explained that Hannah was bipolar and struggling with the death of their cat. Otherwise, Jennifer insisted, the children loved their new home just as they loved spontaneous adventures. The children nodded.

“She was so convincing,” Ms. DeKalb, 59, said of Jennifer.

Still, Ms. DeKalb was worried. In the months that followed, none of the Hart children would speak with her when she tried to talk with them.

Then, in March 2018, Devonte began going to the DeKalb residence requesting food.

Devonte told the DeKalbs his parents were withholding food as punishment, but would ask them not to tell his “mom” that he was visiting, Ms. DeKalb said. When she asked which mother, he explained that there was “Mom and Sarah” — and that “Mom” was responsible for the abuse. Sarah “didn’t used to go along with it,” Devonte told Ms. DeKalb, but was now “tolerating” Jennifer’s behavior.

“I absolutely, from the bottom of my heart, trust what he said,” Ms. DeKalb added.

Devonte also asked that the DeKalbs not call the police because he feared the family would get split up. But later in March, Ms. DeKalb told him she was going to. The next night, when Devonte visited, she said he asked, “Have you called yet?”

She would later grapple with a dark thought: “Because I reported, they took off and killed these kids.”

Concerned co-workers

There was nothing unusual about Sarah’s behavior that Friday, one of her co-workers at Kohl’s told investigators. But several colleagues would later recall that she had previously made odd complaints about her children and became visibly distraught when taking calls from her wife.

Sarah told them that her children “could not function on their own,” had “food issues” and were not allowed in the kitchen.

An assistant manager also said Sarah “would be very concerned” if Jennifer texted or called her at work, sometimes exiting the room in a panic and tearing up during heated phone calls.

Sarah told that manager that Jennifer struggled with depression and mentioned to another co-worker that Jennifer “would stay in bed and cry all the time.” A close relative of Jennifer’s was said to have “concerns about Jennifer’s state of mind,” documents show.

The assistant manager told the authorities about a conversation with Sarah that stood out: Sarah once said she wished that someone had “told her it was O.K. not to have a big family.”

“Then,” Sarah told her boss, “she and Jennifer would not have adopted the children.”

Even with so much going on at home, a manager told investigators, Sarah had “never failed to show up for work.”

Video reviewed by investigators showed Sarah Hart leaving Kohl’s around 5:26 p.m. on March 23 in a white Pontiac. A child welfare official responding to Ms. DeKalb’s call that morning arrived at the Hart home about 10 minutes before that and saw a gold S.U.V. come up the driveway and pull up to the Hart home, according to a report. So the caseworker knocked on the front door. No answer. She left her business card.

Just before 3 a.m. the next day, records show, Sarah Hart texted at least three co-workers: “I thought I would be able to go to work but I’m too sick to come in.”

The authorities later reviewed video of what appears to be Jennifer at a Safeway on the morning of Sunday, March 25. The supermarket was about 25 miles from the Juan Creek crossing on Highway 1.

Investigators returned to the Harts’ home in Washington State the next day. The gold S.U.V. was gone; a German tourist would spot it a few hours later, upside down on a rocky shoreline, more than 500 miles down the Pacific Coast.